A semiconductor LED can be made very thin, such as under 50 microns, to maximize its light output. The semiconductor LED may also have a relatively thick phosphor layer over its top surface to wavelength-convert the light from the LED, such as for creating white light using a blue LED. Such a structure may still only have a total thickness of about 0.2-0.5 mm and a top area of less than 1 mm2. The LED may be a flip chip that is bonded to metal pads on the top surface of a much larger submount so that only the robust electrodes on the bottom of the submount need to be soldered to a printed circuit board.
It is known to surround the LED (but not the submount) with a molded parabolic reflector by inserting the LED through a rectangular opening at the bottom of the reflector. Since the reflector should ideally reflect all light that is emitted from the top and sides of the LED, the inner edge of the reflector closest to the LED needs to have an extremely small thickness (called a knife edge) to capture most of the side light. Further, the ideal reflector should substantially abut the edge of the LED to capture the most side light. Such an ideal reflector is impractical to produce, and typical molded reflectors have varying spaces between the reflector edge and the LED, and the reflector inner edge (about 0.5 mm minimum thickness) blocks most of the side light from entering the reflector area.
What is needed is a technique that enables a practical molded reflector to substantially reflect all light that is emitted from an LED.